Effect of reduction of mobile communications co‐channel interference by transmission power control considering received signal level correlations

In a small-zone mobile communications system that reuses the same frequencies in geographically different places, the margin for interference required to obtain a required call quality (CIR margin) can be reduced when there are correlations between geographic variations of the desired and interfering waves in comparison to when there are no correlations. In a sector zone configuration allowing the arrival directions of desired and interfering waves to be the same direction, correlational relationships can be expected in the downlink circuit, while such relationships cannot be expected in the uplink circuit since the topographical and geological factors affecting the mobile stations are clearly different. In this paper, it has been clarified analytically that when there are correlations between geographic variations of desired and interfering waves of the downlink circuit, the CIR margin can be reduced even in the uplink circuit as well as in the downlink circuit by using adaptive transmission power control (ATPC). Next, the direction connecting the base station and the reception point is defined as the direction of arrival of the electric current and the correlational relationships between the arrival angle difference and the received signal level were studied on the basis of propagation test results, considering the differences in angles of the directions of arrival of desired and interfering waves in the downlink circuit (referred to as the arrival angle differences). In addition, the relationships between the spatial frequency utilization rate (spectrum efficiency) and the sector zone divisions of a wireless zone, closely related to the arrival angle differences, in a six-wave interfering system having six interfering zones have been clarified.